Methyl bromide. It's a toxic substance on the greenhouse gas and ozone-depleting lists.
The world doesn't want it but, conversely, much of the world - and certainly New Zealand - can't seem to do without it.
The odourless, colourless gas is a pesticide used to treat log and wood pulp exports out of New Zealand.
This country is the world's highest user of it and nowhere in NZ is it used more than at Northport's log shipping yards.
It has to be done, or some kind of fumigation must, for the biosecurity of trading partner countries; just as incoming goods are meant to be clean of bugs.
To give an idea of how much of the controversial gas is used, a mandatory annual report to the Environmental Protection Authority (EPA) showed 2355 fumigations at Northport in 2015, using 290,807kg of methyl bromide. In that year, 2.5 million tonnes of logs were shipped out from there.
On behalf of log exporters, Genera Ltd does methyl bromide treatment at several New Zealand ports, and at some industrial sites.
At Northport, the gas is pumped under plastic tarpaulins covering long rows of stacked logs, those covers taken off once the toxic gas has done its work.
Any residue is dispersed into the air. That practice is at the heart of the anti-methyl bromide argument and is also a multi-million dollar poser for lumber exporters and buyers, environmental and hazardous substance authorities, other interest groups, and - not least - Genera.
No one really wants to use the stuff and Genera itself is putting up serious funding for research into alternatives.
It's not all altruism; it is in the company's best interest to be in a good position when and if the plug gets pulled on methyl bromide.
In 2011 the Environmental Risk Management Authority (ERMA) introduced new rules and said "recapture" technology must be used for all fumigations by 2021.
That is some pressure when a more practical, affordable method isn't in sight and any fumigation not acceptable to our foreign markets could be devastating for Northland.
No one wants that, says everyone involved. Yet, whether we can live with or without methyl bromide has been the subject of extensive debate and scientific study for generations.
THE PLASTIC tarpaulin system is approved by Northport via its hazardous substances consent, land use consents-issuer Whangarei District Council, Northland District Health Board and the EPA.
Exporters and Genera say they are impressed with the way Northport deals with its major log shipping role, and its safeguards and checks.
Likewise, Northport is happy with Genera's strict code of operations.
Methyl bromide's use is carefully reported and monitored, and, according to paperwork provided to EPA (by Genera), there have been no "serious" breaches of operational safety at the port.
However, there were two accidental releases recorded in Genera's 2015 report.
One was when a log dropped on a tarpaulin tore a hole in it during a gas-drench; the other when a "strong gust of wind from the west" lifted a corner.
There were no workers at risk either time and no gas detected in the atmosphere during immediate monitoring, the report said.
Whatever was going on inside the treatment zone when a log was dropped was an operational breach in itself, but not to do with the gas treatment protocols.
As for the second incident, it's unsurprising no gas was detected outside the 50 metre buffer zone after a gust from the west had blown any leak straight out to sea.
Both cases highlight weaknesses of the wrap method. Ports of Auckland recently declared it will stop emissions of methyl bromide into the air by the end of this year.
The Port of Tauranga earlier decided to stop venting to air after the business has been done under tarpaulins, with a new filtering system expected to be in use there by 2019.
There is little information at this stage but much research going on about how recaptured material will be disposed of, and much debate among stakeholders in the methyl bromide dilemma about how problematic any disposal will prove to be.
No one wants to send another ozone-depleting gas into the air, put it in the ground or sink concrete containers of the still active industrial waste in the ocean.
Genera Group chief executive Mark Self said the gas's absorption onto carbon "makes carbon a suitable medium for the front end of a fumigant recapture and destroy system".
"Sucking onto carbon filters does not neutralise or render methyl bromide harmless or inert. It concentrates it, enabling one to do something with it," he said.
But do what? That is part of the Genera research programme, which includes scientists working on what kind of recapture method might be suitable at the sprawling Northport log yards.
Back to those 2.5 million tonnes of logs leaving Northland and the fumigation problem that has grown at the same rate as the exports.
In 2001, Genera pioneered in-transit fumigation of logs being shipped to China, using the gas phosphine.
"This method takes advantage of the sealed holds and the long time duration of the voyage to China, using a low dose of phosphine gas to fumigate logs," Self said.
After fumigation the phosphine is vented at sea where it breaks down within 24 hours to form harmless phosphates.
"This technique reduced methyl bromide use for log fumigations by 80 per cent. However, as volumes of log exports have grown, the remaining 20 per cent used for logs carried on ships' decks and for markets that will not accept phosphine fumigation has become a significant amount of gas."
Auckland is not a log port and methyl bromide is used minimally there in the open, so the no-venting-to-air gesture may have been comparatively easy to make.
Nevertheless, it is welcomed by Martime Union of New Zealand (MUNZ) which doesn't like its workers having to breathe in or handle the poison. The union continues to call for a total ban of methyl bromide.
Northland president John Farrow said the union regularly asks for safety assurances, options, to be kept up to date with developments, to be given good information.
"No one wants to use this stuff but, apparently, there isn't much alternative, and we do need to really seriously consider what it might be replaced with," he said.
Mr Farrow said the union did not want to jeopardise Northland's important timber industry, the local economy or any jobs.
"We need to be very considerate and thoughtful. We know they have strict procedures and compliance in place but its safety always needs to be challenged.
"As a union we don't support methyl bromide's use or certainly the method it is used at Northport. We would like to see a better system in place, or a better product.
"But, it could be a case of sticking it the devil you know," Mr Farrow said.
Methyl bromide's inclusion in the ban list of the 1987 Montreal Protocol (for ozone depletion) was left with an open ended phase-out time. Under the Montreal Protocol, using methyl bromide to fumigate soil - once common in New Zealand - was revoked, but its quarantine use and pre-shipment (QPS) treatment of goods is permitted.
During research for this article, apart from the union concerned foremost with workers' wellbeing, although Farrow also referred to the environmental quandary, all parties said the concern was less about human health than the ozone layer.
Methyl bromide has been at the centre of health scares. In 2010 MUNZ called out Port Nelson over concerns about a disproportionately high number of motor neurone disease cases among workers.
The link was never proved, but it remains lodged in the debate.
Despite the dollars and decades spent on the "conundrum", no one - anywhere - has found an effective, affordable alternative pesticide to meet some countries' fumigation requirements.
The EU is dead against the stuff but other log importers, such as India, will accept nothing else. China accepts several options, methyl bromide among them.
When it comes to using it to treat New Zealand's valuable timber exports, everyone in the business says they're dammed if they do and dammed if they don't.
The pan-industry group Stakeholders in Methyl Bromide Reduction (STIMBR) has identified the non-greenhouse gas ethanedinitrile (EDN) as a possible alternative but the EPA has yet to approve its use.
Don Hammond, STIMBR president, reiterated methyl bromide's contribution to ozone depletion and its greenhouse gas role above secondary international concerns about its effect on human health.
"The global community has only allowed methyl bromide because there is no alternative," Hammond said.
"It's very important that we protect the export [log] market. We also understand this is a toxic gas, and we have to be excessively careful.
``It's not about saying it's an acceptable level of risk, because we can't have one person at risk.
But we've spent a lot of money and time trying to find the silver bullet to fix the problem and it looks like all we've found is that methyl bromide itself could be the silver bullet."